Electrosurgical instruments have been used in high-frequency surgery for many years to coagulate or to cut biological tissue. In the case of a coagulation, a high-frequency (“HF”) current is conducted through the tissue to be treated so that it changes due to protein coagulation and dehydration. In this case, the tissue contracts such that the vessels are closed and bleeding is stopped. A cutting process requires a high current density so that the tissue is completely cut through by an explosive evaporation of the tissue fluid and an associated ripping open of the cell membranes.
Both monopolar and bipolar techniques are used for the thermal treatment of biological tissue.
In the case of the monopolar technique, the HF current supplied by a HF generator to the electrosurgical instrument is applied into the tissue to be treated by means of an active electrode, the current path through the body of a patient leading to a passive neutral electrode and from there back to the HF generator. A high current density per surface unit is provided for treatment at the active electrode, while in the case of the neutral electrode the current density per surface unit is significantly reduced in comparison to the active electrode. This can be achieved by designing the neutral electrode with a correspondingly large surface. Monopolar cutting is particularly suitable for large cuts, for example, to cut through fat tissue.
The bipolar technique is used when the HF current should be applied with high precision. Bipolar instruments generally have two clamping parts connected to one another in an articulated manner, handle devices for handling the clamping parts being provided at their proximal ends. Electrode parts for conducting the HF current from the HF generator through the tissue to be treated are located at distal ends of the clamping parts. To this end, the electrode parts can be connected via power supply devices to the HF generator. The electrode parts are usually designed in such a manner that they are also suitable for holding and clamping the tissue to be treated. Due to the short current path between the electrode parts of the bipolar instrument, the current path can be better calculated than in the case of monopolar arrangements since it does not run long distances through the body of the patient.
WO 99/37228 discloses a bipolar coagulation and cutting device for endoscopic surgery. Two branches are provided which can be moved by means of an axially displaceable tube part. The branches have flat coagulation electrodes which are respectively formed on the inside with a hole area and which are opposite one another at distal ends in order to hold and coagulate a tissue to be treated with these. Moreover, a rod-shaped cutting electrode is provided which can also be moved by means of the tube part and which attacks the clamped tissue between the coagulation electrodes through the hole area. As a result of a successive linear displacement of the tube part, the cutting electrode—similar to the cut made by scissors—moves ever closer to the tissue to be treated until it has completely covered the desired cutting line.
The cutting area of the cutting electrode of an electrosurgical instrument is both in the case of the monopolar and in the case of the bipolar technique, as shown with WO 99/37228, constantly exposed to high stresses since a high current density required for the cutting process at the electrode promotes wear of the electrode.
Other electrosurgical instruments provide cutting electrodes of extremely small design (e.g. needle electrode) such that a simultaneous coagulation cannot be sufficiently carried out due to small coagulation surfaces. Particularly in the case of hollow organs such as blood vessels, it is thus very difficult to perform a targeted thermofusion.
Electrosurgical instruments are often formed with a cutting edge which must be activated mechanically. After successful coagulation, the treated tissue can be completely cut through by means of the cutting edge. The force which has to be applied by the surgeon in this case during cutting also brings about a high degree of wear of the cutting edge with the result that the quality of the cut is significantly reduced after only a short time. The cutting electrode must therefore be replaced on a frequent basis, which is often difficult as a result of relatively complex mechanics. In some cases, it may even no longer be possible to use the entire electrosurgical instrument and it must therefore be completely replaced.